By default, trace/cluster/ServiceRuleWatchMaxProductionLevelis set to 4 unless it has modified. Please compare with system level setting. If it is higher we won't see Trace option for Service-Email rule.
P.S: I tried in my local by altering the setting. I could observe the issue reported.
Can you check the production level of your system ? To see the Trace option for service rules, your system production level should be less than or equal to the value set in the DSS "trace/cluster/ServiceRuleWatchMaxProductionLevel".